FIX: Call to managed class method with StringBuilder as in or out parameter may fail (317577)

RESOLUTION

1. Use IntPtr instead of System.Text.StringBuilder to build a modified managed server, as follows:

   using System;
   using System.Text;
   using System.Runtime.InteropServices;
   namespace Q317577 {
         public interface ITest{
               void Test(ref IntPtr sbString, ref int length);
         }
         public class Class1 : ITest{
               public Class1(){
               }
               public void Test(ref IntPtr sbString, ref int length){
                    Marshal.FreeCoTaskMem(sbString);
                    string str = "changed changed";
                    length = str.Length;
                    sbString = Marshal.StringToCoTaskMemUni(str);
               }
         }
   }
   					

2. Use Regasm.exe to register the server, as follows:

   #include <stdio.h>
   #include <tchar.h>
   #import "Q317577.tlb" no_namespace named_guids
   
   int _tmain(int argc, _TCHAR* argv[])
   {
         CoInitialize(NULL);
         try{
               ITestPtr spTest;
               //wchar_t wszTestString[] = L"This is a test.";
               wchar_t wszTestString[] = L"A long long string for test.";
               long length = (wcslen(wszTestString) + 1) * sizeof(WCHAR);
               LPWSTR lpszTestString = (LPWSTR)::CoTaskMemAlloc(length);
               spTest.CreateInstance(CLSID_Class1);
               wcscpy((LPWSTR)lpszTestString, wszTestString);
               spTest->Test((long*)&lpszTestString,&length);
               MessageBoxW(NULL, (LPWSTR)lpszTestString, L"Results", 0); 
               ::CoTaskMemFree((LPWSTR)lpszTestString);
         }
         catch(_com_error cerr){
               MessageBox(NULL, cerr.Description(), "err", 0); 
         }
         CoUninitialize(); 
         return 0;
   }
   					

1. In the IntOpTst Property Pages dialog box, click Configuration Properties, and then click Build. Change the Register for COM Interop value to True.
2. Modify the unmanaged client code to make a call to the managed server.